1. Field of the Invention
The present invention relates to electrically actuated power door locks for automotive vehicles. More particularly, the present invention relates to a power door lock actuator of the motor drive type which provides increased reliability and improved mechanical function as compared to prior power door lock actuators.
2. Description of the Related Art
Power door locks have become ubiquitous in motor vehicles, especially with the advent of remote engine systems. Power door locks provide electrical actuation of the door lock mechanism of a motor vehicle in response to a user pressing a switch.
There are two basic mechanisms that can provide power door lock actuation: a solenoid and a motor drive. Because solenoids are frequently noisy and sometimes actuation is unreliable, motor drives have become the actuator of choice.
Various motor drive type door lock actuators have been proposed and installed on production motor vehicles. A motor drive typically includes an electric motor, a gear set and an actuation mechanism responsive to the electric motor via the gear set. Problematical, however, is the situation when the user uses his or her key to unlock his or her car door lock, since the motor drive would then be back-driven and thereby offer unacceptable resistance to turning the key. This situation also arises when the user manually actuates the door lock button on the door. It has become known that a solution to the problem of the motor drive being back driven during manual and key operation of the door lock is to provide "lost motion" in the motor drive.
Following are descriptions of some interesting prior motor type door lock actuators. U.S. Pat. No. 4,819,493 describes the use of an inertial clutch to couple a rack and pinion gear set to the motor only when the motor is operating. U.S. Pat. No. 4,674,781 describes another rack and pinion gear set having a lost motion coupling wherein a pair of opposing springs return the rack to a neutral position between spaced apart, opposing abutments when the motor is turned off. Finally, U.S. Pat. No. 4,893,704 describes main and secondary threaded shafts with opposed threads that cooperate to axially move a drive member, wherein lost motion is provided by pins running free in a slot until one end or the other of the slot is encountered.
In spite of the many attempts in the art to provide an acceptable power door lock actuator, there yet remains needed a mechanically simple and reliable power door lock actuator which also solves the back driving problem when the door lock mechanism is manually actuated.